(Roughly) Daily

Posts Tagged ‘astrophysics

“‘Space-time’ – that hideous hybrid whose very hyphen looks phoney”*…

Space-time curvature [source: ESA]

Space and time seem about as basic as anything could be, even after Einstein’s theory of General Relativity threw (in) a curve. But as Steven Strogatz discusses with Sean Carroll, the reconciliation of Einstein’s work with quantum theory is seeming to suggest that space and time might actually be emergent properties of quantum reality, not fundamental parts of it…

… we’re going to be discussing the mysteries of space and time, and gravity, too. What’s so mysterious about them?

Well, it turns out they get really weird when we look at them at their deepest levels, at a super subatomic scale, where the quantum nature of gravity starts to kick in and become crucial. Of course, none of us have any direct experience with space and time and gravity at this unbelievably small scale. Up here, at the scale of everyday life, space and time seem perfectly smooth and continuous. And gravity is very well described by Isaac Newton’s classic theory, a theory that’s been around for over 300 years now.

But then, about 100 years ago, things started to get strange. Albert Einstein taught us that space and time could warp and bend like a piece of fabric. This warping of the space-time continuum is what we experience as gravity. But Einstein’s theory is mainly concerned with the largest scales of nature, the scale of stars, galaxies and the whole universe. It doesn’t really have much to say about space and time at the very smallest scales.

And that’s where the trouble really starts. Down there, nature is governed by quantum mechanics. This amazingly powerful theory has been shown to account for all the forces of nature, except gravity. When physicists try to apply quantum theory to gravity, they find that space and time become almost unrecognizable. They seem to start fluctuating wildly. It’s almost like space and time fall apart. Their smoothness breaks down completely, and that’s totally incompatible with the picture in Einstein’s theory.

s physicists try to make sense of all of this, some of them are coming to the conclusion that space and time may not be as fundamental as we always imagined. They’re starting to seem more like byproducts of something even deeper, something unfamiliar and quantum mechanical. But what could that something be?….

Find out at: “Where Do Space, Time and Gravity Come From?, ” from @stevenstrogatz and @seanmcarroll in @QuantaMagazine.

* Vladimir Nabokov

###

As we fumble with the fundamental, we might send far-sighted birthday greetings to Jocelyn Bell Burnell; she was born on this date in 1943. An astrophysicist, she discovered the first pulsar, while working as a post-doc, in 1957. She then discovered the next three detected pulsars.

The discovery eventually earned the Nobel Prize in Physics in 1974; however, she was not one of the prize’s recipients. The paper announcing the discovery of pulsars had five authors. Bell’s thesis supervisor Antony Hewish was listed first, Bell second. Hewish was awarded the Nobel Prize, along with the astronomer Martin Ryle.

A pulsar— or pulsating radio star– a highly magnetized, rotating neutron star that emits a beam of electromagnetic radiation. The precise periods of pulsars make them very useful tools. Observations of a pulsar in a binary neutron star system were used to  confirm (indirectly) the existence of gravitational radiation. The first extrasolar planets were discovered around a pulsar, PSR B1257+12.  And certain types of pulsars rival atomic clocks in their accuracy in keeping time.

Schematic rendering of a pulsar

source

Jocelyn Bell Burnell

source

Written by (Roughly) Daily

July 15, 2022 at 1:00 am

“I’m sure the universe is full of intelligent life. It’s just been too intelligent to come here.”*…

Email migration should now be complete; email subscribers should now be getting (Roughly) Daily via Mailchimp, and should not be getting a duplicate from Feedburner. If you are getting a dupe, please let me know (roughlydaily@gmail.com). Note that this new service may be landing in your Gmail “Promotions” folder; you can move it to your main folder. With apologies for the turbulence over the last few days, and thanks for your continued reading, on to today’s post…

A new computer simulation shows that a technologically advanced civilization, even when using slow ships, can still colonize an entire galaxy in a modest amount of time. The finding presents a possible model for interstellar migration and a sharpened sense of where we might find alien intelligence.

Space, we are told time and time again, is huge, and that’s why we have yet to see signs of extraterrestrial intelligence. For sure, the distances between stars are vast, but it’s important to remember that the universe is also very, very old. In fact, I’d go so far as to say that, in terms of extremes, the Milky Way galaxy is more ancient than it is huge, if that makes sense. It’s for this reason that I tend to dismiss distances as a significant variable when discussing the Fermi Paradox—the observation that we have yet to see any evidence for the existence of alien intelligence, even though we probably should have.

New research published in The American Astronomical Society is bolstering my conviction. The new paper, co-authored by Jason Wright, an astronomer and astrophysicist at Penn State, and Caleb Scharf, an astrobiologist at Columbia University, shows that even the most conservative estimates of civilizational expansion can still result in a galactic empire.

A simulation produced by the team shows the process at work, as a lone technological civilization, living in a hypothetical Milky Way-like galaxy, begins the process of galactic expansion… Things start off slow in the simulation, but the civilization’s rate of spread really picks up once the power of exponential growth kicks in. But that’s only part of the story; the expansion rate is heavily influenced by the increased density of stars near the galactic center and a patient policy, in which the settlers wait for the stars to come to them, a result of the galaxy spinning on its axis.

The whole process, in which the entire inner galaxy is settled, takes one billion years. That sounds like a long time, but it’s only somewhere between 7% and 9% the total age of the Milky Way galaxy.

As noted, the new model is constrained by some very conservative rules. Migration ships are launched once every 10,000 years, and no civilization can last longer than 100 million years. Ships can travel no farther than 10 light-years and at speeds no faster than 6.2 miles per second (10 kilometers per second), which is comparable to human probes like the Voyager and New Horizons spacecraft. 

“This means we’re not talking about a rapidly or aggressively expanding species, and there’s no warp drive or anything,” said Wright. “There’s just ships that do things we could actually manage to do with something like technology we can design today… Even under these conditions, the entire inner part of the simulated galaxy became settled in a billion years. But as Wright reminded me, our “galaxy is over 10 billion years old, so it could have happened many times over, even with those parameters.”…

A new simulation published by the American Astronomical Society suggests that aliens wouldn’t need warp drives to take over an entire galaxy in (relatively) short order, as George Dvorsky (@dvorsky) explains.

[Image above: Andromeda Galaxy, source]

* Arthur C. Clarke

###

As we spread out, we might spare a thought for Jacobus Cornelius Kapteyn; he died on this date in 1922. An astronomer, he used photography and statistical methods to determine the motions and spatial distribution of stars (especially with the Milky Way), the first major step after the works of William and John Herschel. He introduced absolute magnitude and color indexing as standard concepts in cataloguing stars.

Kapteyn was also among the first to suggest the existence of dark matter (which he deduced from examining stellar velocities).

source

“Oh, there you are Peter”*…

 

The missing links between galaxies have finally been found. This is the first detection of the roughly half of the normal matter in our universe – protons, neutrons and electrons – unaccounted for by previous observations of stars, galaxies and other bright objects in space.

You have probably heard about the hunt for dark matter, a mysterious substance thought to permeate the universe, the effects of which we can see through its gravitational pull. But our models of the universe also say there should be about twice as much ordinary matter out there, compared with what we have observed so far.

Two separate teams found the missing matter – made of particles called baryons rather than dark matter – linking galaxies together through filaments of hot, diffuse gas

Get galactic at: “Half the universe’s missing matter has just been finally found.”

* meme

###

As we heed E.M. Forster, we might recall that it was on this date in 1843 that Sir William Rowan Hamilton conceived the theory of quaternions.  A physicist, astronomer, and mathematician who made important contributions to classical mechanics, optics, and algebra, he had been working since the late 1830s on the basic principles of algebra, resulting in a theory of conjugate functions, or algebraic couples, in which complex numbers are expressed as ordered pairs of real numbers.  But he hadn’t succeeded in developing a theory of triplets that could be applied to three-dimensional geometric problems.  Walking with his wife along the Royal Canal in Dublin, Hamilton realized that the theory should involve quadruplets, not triplets– at which point he stopped to carve carve the underlying equations in a nearby bridge lest he forget them.

 source

 

Written by (Roughly) Daily

October 16, 2017 at 1:01 am

“It’s the end of the world as we know it”*…

 

“The probability of global catastrophe is very high,” the Bulletin of the Atomic Scientists warned in setting the Doomsday Clock 2.5 minutes before midnight earlier this year. On nuclear weapons and climate change, “humanity’s most pressing existential threats,” the Bulletin’s scientists found that “inaction and brinkmanship have continued, endangering every person, everywhere on Earth.”

Every day, it seems, brings with it fresh new horrors. Mass murderCatastrophic climate changeNuclear annihilation.

It’s all enough to make a reasonable person ask: How much longer can things go on this way?

A Princeton University astrophysicist named J. Richard Gott has a surprisingly precise answer to that question…

Gott applies straight-forward logic and the laws of probability to setting our exit date.  “Calculations” haven’t worked out so well for Mayan seers or the likes of Harold Camping; but as you’ll read, Gott has tested his method, and done remarkably well… so: “We have a pretty good idea of when humans will go extinct.”

* REM

###

As we plan our parties, we might recall that it was on this date in (what we now call) 46 BCE, that the final year of the pre-Julian Roman calendar, began.  The Romans had added a leap month every few years to keep their lunar calendar in sync with the solar year, but had missed a few with the chaos of the civil wars of the late Republic. Julius Caesar added two extra leap months to recalibrate the calendar in preparation for his calendar reform, which went into effect in (what we now now as) 45 BC.  The year, which had 445 days, was thus known as annus confusionis (“year of confusion”).

Fragmentary fresco of a pre-Julian Roman calendar

source

 

 

Written by (Roughly) Daily

October 13, 2017 at 1:01 am

“Magnetism, you recall from physics class, is a powerful force that causes certain items to be attracted to refrigerators”*…

 

Concentric incision on a jar handle from Ramat Rahel, in modern-day Israel

Of all the environmental amenities that this hospitable planet provides, the magnetic field is perhaps the strangest and least appreciated. It has existed for more than three and a half billion years but fluctuates daily. It emanates from Earth’s deep interior but extends far out into space. It is intangible and mostly invisible—except when it lights up in ostentatious greens and reds during the auroras—but essential to life. The magnetic field is our protective bubble; it deflects not only the rapacious solar wind, which could otherwise strip away Earth’s atmosphere over time, but also cosmic rays, which dart in from deep space with enough energy to damage living cells. Although sailors have navigated by the magnetic field for a millennium and scientists have monitored it since the eighteen-thirties, it remains a mysterious beast. Albert Einstein himself said that understanding its origin and persistence was one of the great unsolved problems in physics…

Direct measurements of the magnetic field now span almost two hundred years, and iron-rich volcanic rocks on the ocean floor provide a lower-fidelity chronicle of its erratic behavior—including wholesale reversals in polarity—back about a hundred and fifty million years. But reconstructing the field’s behavior between these two extremes has been difficult. The trick is to find an iron-bearing object that locked in a record of the magnetic field at a well-constrained time in the past, in the way that wine of a given vintage preserves an indirect record of that year’s weather conditions…

Last Monday, in a study published in Proceedings of the National Academy of Sciences, a team of Israeli and American archeologists and geophysicists reports the most detailed reconstruction yet of the magnetic field in pre-instrumental times, using a set of ceramic jars from Iron Age Judea…

In the geophysical community, the tales told by the Judean jars may cause unrest. Both the height and the sharpness of the spike they recount push up against the limits of what some geophysicists think Earth’s outer core is capable of doing. If the eighth-century-B.C. geomagnetic jeté is real, models for the generation of the magnetic field need significant revision. Given the importance of a stable magnetic field to our electricity-dependent, communications-obsessed culture, these questions are of more than academic interest…

More on these befuddling fields at “Earth’s mysterious magnetic field, stored in a jar.”

* Dave Barry

###

As we look for True North, we might send undulating birthday greetings to George Fitzgerald Smoot III; he was born on this date in 1945.  An astrophysicist and cosmologist, Smoot discovered the signature of gravitational waves– ripples in space-time were first predicted by Albert Einstein– in his study of the cosmic microwave (“background”) radiation that originated with the Big Bang.  He won the Nobel Prize in Physics in 2006; three years later he became the second person to run the board on the quiz show Are You Smarter than a 5th Grader?, and took home the $1 million grand prize.

 source

 

Written by (Roughly) Daily

February 20, 2017 at 1:01 am

%d bloggers like this: